I have a constant heartbeat hum in my ear that is louder at night? What is it and how to treat?

Carotid bruit. Occasionally this may be the bruit from a carotid stenosis. I would recommend that you should have a carotid ultrasound to see if there is any carotid disease.
Carotid stenosis. Need to be checked for narrowing of your carotid artery. Usually a simple ultrasound.